Apparatus for the determination of interior ballistics



Nov. 6, 1962 E. L. ARMI ETAL 3,062,047

APPARATUS FOR THE DETERMINATION OF INTERIOR BALLISTICS 2 Sheets-Sheet 1 Filed June 26, 1952 FIG. I

4a W g 44 x 60 j .I/ INVENTORS EDGAR L. ARM/ JAMES L. JOHNSON RAYMOND 6. MACHLER 261g gIjMAN E. POLSTE'R @/3 W ATTORNEYS Nov. 6, 1962 E. ARMI ETAL 3,062,047

APPARATUS FOR THE DETERMINATION OF INTERIOR BALLISTICS Filed June 26, 1952 2 Sheets-Sheet 2 24 IHIIII mum FIG. 2 F763 INVENTORS EDGAR L. ARM! JAMES L JOHNSON RAYMOND 0. MAOHLER NORMA/V E. POLSTER @73 ATTORNEYS United States Patent Office 3,062,047 Patented Nov. 6, 196 2 3,062,047 APPARATUS FOR TEE DETERMINATION 9F KNTERIQR BALLISTKQS Edgar L. Arrni, Santa Monica, (Iaiifl, and James L. liohnson, Upper Darby, Raymond C. Machler, Phiiadelphia, and Norman E. Polster, Southampton, Pa, assignors, by mesne assignments, to the United States of Ame ica as represented by the Secretary of the Navy Filed June 2a, 1952, Ser. No. 295,624 3 Claims. (Ci. 73-167) This invention relates to an apparatus for conducting interior ballistic tests and more particularly to an apparatus for determining heat conditions produced by movement of a projectile through a gun barrel.

In order to efiiciently design a gun knowledge is required of all characteristics of interior ballistics, however, one characteristic of interior ballistics that has not heretofore accurately been measured is the frictional heat and temperature generated solely by a bullet as it is projected through the barrel of a gun. Although past methods and apparatus have made it possible to determine the total heat input to a gun barrel when a projectile is fired, the information determined thereby has included heat transferred to the barrel from hot powder gases. The present invention contemplates providing an apparatus for determining that increment of total heat generated soley by the frictional contact between the bullet or projectile and the gun barrel, and furthermore to provide a means for determining the temperature at the interface between the bullet and the gun barrel bore.

With the foregoing in mind it is an object of the present invention to provide an apparatus for determining the frictional heat generated by a bullet as it is projected through the barrel of a gun.

Another object of this invention is to provide means for determining the frictional interface temperature between a moving bullet and a bore of a gun barrel.

Still another object of the invention is the provision of a device wherein a bullet may be forced through a gun barrel by controlled mechanical means.

Another object is to provide a sliding thermocouple.

A further object is the provision of a novel means for determining the temperature of the contact point of elements moving relative to each other.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a test stand embodying the present invention;

FIG. 2 is a vertical cross section of the embodiment illustrated in FIG. 1 wherein a bullet is shown positioned in one end of a section of gun barrel preparatory to being rammed therethrough; and

FIG. 3 is a vertical cross section of a modification of the embodiment illustrated in FIG. 2.

Referring now to the drawings, in which like numerals designate the same parts throughout the several views, and more particularly to FIGS. 1 and 2, wherein there is illustrated a device constructed in accordance with the present invention and comprising a base having a central aperture 11 therein and mounting an upwardly extending bushing or sleeve 12. The sleeve 12 has a central passageway 13 coaxial with the aperture 11 through the base 10, and is counterbored or enlarged at its upper end to receive the lower portion of a barrel section enclosing cylinder 14. The cylinder 14 is adapted to receive within its interior a gun barrel section 17, which is supported therein in coaxial alignment with the passageway 13 by means of upper and lower barrel guide bushings 18 and 19, respectively. The upper portion of the barrel section enclosing cylinder 14 is axially bored at 20 to receive a plunger or projectile engaging piston 21 which is slidably mounted therein for reciprocal movement to drive a projectile 22 through the gun barrel section 17. The projectile is provided with a shock absorbing disk 23, which may be formed of steel or the like, which distributes the shock produced by the contact of piston 21 to prevent an excessive deformation of the after portion of the projectile, which might affect the accuracy of the test being conducted thereon. The projectile Z2 is electrically insulated from cylinder 14 by means of a sleeve 26, which may be Bakelite or the like, and a disk 27 made of a similar material which is secured on the underside of the piston 21 and in a position to contact the shock absorbing disk 23 mounted on the projectile. The downward movement of the piston 21 is limited by the engagement of an enlarged head portion 24 thereof with an annular ring 25, which may be composed of resilient material such as rubber and the like, positioned on the top of the cylinder 14 and concentric with the body of the piston.

The piston or plunger 21 is urged downwardly into contact with the projectile 22 by means of an impact delivering means, indicated generally by the numeral 30 (FIG. 1), which in the embodiment illustrated comprises a weight supporting platform 31, which may be of circular configuration, having a plurality of vertically disposed reinforcing webs 32 mounted on the underside thereof in any well-known manner. Secured to opposite peripheral edges of the platform 31 are a pair of upright rods 33, which are strengthened and supported relative to the platform 31 by means of diagonally disposed braces 34 and are interconnected at the upper ends by a cross brace 35. Mounted on the cross brace 35 intermediate of the ends thereof is a carriage holding and release mechanism which is adapted to positively engage a lifting cable 41 for raising the impact delivering means or carriage 30 to a predetermined position above the piston or plunger 21. The mechanism 40 may be either electrically or mechanically operated to release the carriage 30 from the cable 41 and thereby permit an impact to be delivered to the piston 21 by the carriage.

The reciprocal movement of the carriage 30 is controlled in a linear path by a pair of vertically extending guide lines or cables 42 which are connected at their lower ends by means of wire rope socket and thimble assemblies 43 to suitable screw eyes 44 mounted on the base member 10 and connected at their upper ends in a similar manner to a suitable overhead support (not shown). The carriage 30 is slidably connected to the guide wires 42 by means of a plurality of outwardly extending brackets 45 mounted in spaced relationship on the vertically extending rods 33 of the carriage and encompassing the guide wires to provide therewith a stabilizing means to prevent the carriage from swaying lateral- 1y at its descends at high speed toward the plunger or piston 21.

A horizontally disposed piston engaging bar is mounted on the bottom portions of the webs 32 which support the platform 31. The carriage 30 is arrested in its downward movement by stops 51 which include a pair of cylindrical members or pillows 52 mounted on the base 10 and composed of any strong metal such as steel. Mounted on the top of the pillows 52 is a pair of shock absorbers 53 formed of lead or any other similar deformable metal, each of which is disposed beneath the piston engaging bar '50 to be contacted thereby to absorb the excessive kinetic energy not consumed in forcing the bullet 22 through the bore of the gun barrel section 17.

The velocity at which the bullet 22 traverses the barrel section 17 may be varied either by regulating the height from which the carriage 30 falls or by adding additional weight on the platform 31, or both, thereby imparting any predetermined amount of kinetic energy to the bullet 22. Thus, it is apparent that the velocity at which the bullet 22 traverses the barrel section 17 can be controlled, and that it will therefore be possible todetermine, as hereinafter described, heat input to the barrel section 17 and interface bullet-bore temperature as a function of bullet velocity.

Determination of Frictional Heat Input To determine the frictional heat input to a gun barrel caused by the movement of a bullet therethrough, the barrel portion 17 may be considerably shorten-ed from its normal length. A suitable aperture is formed through the wall of the cylinder 14 to accommodate electrical leads 60 and 61 (FIG. 2). The leads 60 and 61 have their respective ends peened or otherwise secured into the barrel section 17 to form the hot junction terminals of a thermocouple 62.. The opposite ends of leads 60 and 61 are connected at their other ends to an electrosensitive measuring instrument 64 such as a millivoltmeter, potentiometer, or the like which may be calibrated in degrees of temperature.

In operation the weight of the carriage 39 is increased if so desired by the placing of bars or blocks of metal on the platform 31 and then the carriage is raised to a predetermined height by means of a lifting cable 41.

The carriage 30 may be released by actuating the release mechanism 40, to move downwardly to contact the plunger head 24 and thereby cause the bullet 22 to traverse the barrel section 17. The passage of the bullet 22 through the barrel section 17 causes heat to be generated due to the frictional contact between the bullet and the barrel section. This heat, which is absorbed by the barrel section 17, is transformed to electromotive force by the thermocouple and is indicated in degrees of temperature by the measuring instrument 64. The temperature, indicated by the instrument 64, is the total heat input to the barrel section 17 generated solely by the movement of a bullet 22 therethrough. This total heat input may be transformed to heat input per unit area of the section by means of a formula well-known in the art: b

where H is the heat input per unit area of the bore, b

the wall thickness of the barrel section, d the bore diameter, c the specific heat, and p the density of the barrel section material. By varying the weight of the impact delivering carriage and the height from which it may fall to strike the plunger 21 a plurality of readings of heat input may be obtained from the temperature indicating means and plotted graphically as a function of velocity of the projectile 22 which velocity is substantially that of the impact delivering carriage. The function obtained thereby may be extrapolated to determine heat input produced by projectile velocities far greater than those obtainable by the impact means alone, thereby making possible a simulation of conditions existing during actual firing of a projectile through the barrel of a gun in which the projectile velocity will be dependent upon the size of the propellant charge.

Determination of Interface Temperature It is well-known in the art that a conventional thermocouple comprises two junctions of dissimilar metals and that each junction is a seat of an electromotive force. When the junctions are at the same temperature, the electromotive forces present are equal and opposite, but when one of the junctions is at a higher temperature than the other a current will flow in a circuit connecting them which current may be measured by an electrosensitive instrument such as a millivoltmeter, potentiometer or a cathode ray oscilloscope. One embodiment of the present invention adapts this principle to the determination of electromotive force developed between bodies which are in sliding contact with each other, which in the present instance are a bullet jacket and a gun barrel.

Referring now to FIG. 3, wherein there is disclosed an apparatus, similar to that shown in FIG. 2, which is modified for the purpose set forth above. The modification includes a flexible electrically conductive lead 70 which is attached on the nose of the bullet 22 at 71 and extends through the mouth of the barrel section 17 and continues through suitable apertures in the cylinder 14 to terminate at one input terminal of an amplifier 72. A second lead 73 connects the barrel section 17 with a second input terminal of the amplifier 72 thereby providing a closed circuit between the input of the amplifier, the bullet 22 and cylinder 17, which comprises a sliding thermocouple.

The output of the amplifier 72 is developed across a load resistor 74 and is measured by means of a cathode ray oscilloscope 75 having horizontal and vertical deflection plates 76 and 77, respectively. The vertical deflection plates 77 are connected across the load resistor 74 by means of leads 78 and 79 to provide a closed vertical sweep circuit for indicating and measuring variations in electromotive force or energy produced by relative movement between the bullet 22 and the barrel section 17. The horizontal deflection plates 76 of the cathode ray oscilloscope 75 are energized by a circuit 80 including a source of potential 81, which may be a battery, and a bayonet type switch 82. The switch 82 is comprised of a pair of cylindrical receptacles 83 each containing a pool of mercury and a pair of spaced electrically interconnected depending prongs 84 (FIG. 1) which are adjustable in length. The receptacles 83 are mounted on the base 10 and the prongs 84 are secured to the undersurface of the movable carriage 30. The prongs 84 and the level of the mercury in the receptacle 83 are so positioned that the prongs will contact the mercury contained thereby closing the horizontal plate energizing circuit 80 the instant that the bar of the carriage 30 engages the head portion 24 of the piston 21.

The operation is very much similar to that of the apparatus previously described in that the bullet 22 having lead attached thereto is placed within the barrel section 17 and the carriage 30, carrying any desired weight, is raised to a predetermined height by means of cable 41. The release mechanism 40 is then actuated to permit the carriage 30 to fall freely toward the piston 21. At the moment the bar 50 of the carriage 30 contacts the head portion 24 of piston 21, the prongs 84 of the switch 82 make contact with the mercury within the receptacles 83 to energize the horizontal plates 76 of cathode ray oscilloscope 75. The carriage 30 continues to move downwardly forcing the piston 21 and the bullet 22 before it. The frictional contact between the bullet 22 and the barrel section 17 causes heat energy to be produced which is transformed by the thermocouple properties of the bullet and barrel section into electromotive energy. This electromotive energy is amplified and appears as a trace on the face of the cathode ray oscilloscope as variations in temperature. The resultant trace of temperature against time may be recorded for further studies by means of photographic or other similar apparatus.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A ballistic device for determining the temperature at the sliding interface between the bullet and the bore of a gun barrel when the bullet is propelled therethrough comprising a housing, a gun barrel portion rigidly supported in the housing, a bullet mounted Within the bore of the portion of gun barrel, a plunger cooperatively engaging said bullet for axial movement therewith, releasable means for imparting positive impact to the plunger, said releasable means being guidingly supported for axial alignment with said plunger, means for varying said impact releasable means so as to force the plunger into the bore to propel the bullet through the barrel at a controlled velocity, a conductor attached to the gun barrel, a second conductor attached to the bullet, and an electromotive-sensitive instrument interconnecting the conductors for indicating the electrornotive force developed at the interface as the bullet is propelled through the gun barrel, said electromotive force being a measure of the temperature at the interface.

2. A ballistic device for determining the interfacial temperature between a bullet and a bore of a gun barrel comprising; a portion of gun barrel, a bullet within said gun barrel, a plunger rod for cooperatively engaging the bullet in axial alignment with the bore of the gun barrel, a releasable freely falling means outside said gun barrel for positively forcing the plunger and bullet through the gun barrel, and means for continuously measuring the electromotive force developed between the bullet and the gun barrel during movement through the gun barrel.

3. A ballistic device for determining the interfacial temperature between a bullet and a bore of a gun barrel comprising; a portion of gun barrel, a bullet within said gun barrel, a plunger rod for cooperatively engaging the bullet and in axial alignment therewith, means outside said gun barrel for forcing the plunger and bullet through the gun barrel, and means measuring the electromotive force developed by the frictional contact between the bullet and gun barrel at the interface therebetween, said electromotive force being a measure of the temperature at the interface.

References Qited in the file of this patent UNITED STATES PATENTS 1,314,801 Hanzlik Sept. 2, 1919 2,365,015 Simmons Dec. 12, 1944 2,377,425 Jackson June 5, 1945 2,445,326 Janney July 20, 1948 2,514,297 Smith et a1. July 4, 1950 2,681,563 Golden June 22, 1954 

